Yahyah Farroukh in a photograph on Facebook. The 21-year-old was arrested on Saturday night.
Photograph: Facebook

Detectives investigating an attempted bomb attack on a London tube train have been granted more time to question two men arrested in connection with the incident who had been fostered by the same couple.

An 18-year-old man arrested in Dover while trying to leave the UK the morning after the attack had been living with a foster couple in Surrey, while a 21-year-old man arrested a few hours later was with the same couple until a few months ago.

On Monday, foster carers Penelope and Ronald Jones, aged 71 and 88, were reported to be staying with friends while police continued to search their home at Sunbury-on-Thames.

Meanwhile a picture was emerging of the 21-year-old, who was named by his employer as Yahyah Farroukh, a Syrian who arrived in the UK as a refugee about four years ago. He was arrested on Saturday night after completing his shift at a chicken takeaway shop in Hounslow, west London.

Scotland Yard said on Monday night that magistrates had granted warrants allowing the 18-year-old to be held until 23 September, and Farroukh until 21 September.

Eyewitnesses said earlier that Farroukh had just left Aladdin’s Fried Chicken and was walking past a bus stop where two plainclothes police officers seized him.

Other officers appeared and took his phone and emptied the contents of his pockets, before placing plastic bags over his hands and feet to preserve any evidence.

Suleman Sarwar, who manages Aladdin’s, said police had searched Farroukh’s locker and taken CCTV footage away from the shop.

“He never seemed like a radical, if anything I thought he was the opposite,” he said. “He seemed very westernised, he was into American rap music and wore western clothes like jeans and T-shirt. He was very sensible and mature.”

A man who said he was friendly with Farroukh when he lived in Syria said he did not believe he had strong religious or political convictions. Though he said he had not seen Farroukh in about four years, the man – who asked not to be named – said he was shocked by the news of the arrest.

He told the Guardian via social media: “He is really good person. Well I would describe him as a good person, friendly and I mean it when I say friendly.”

Asked about Farroukh’s suspected involvement in the terror attack, the man said: “I mean that’s impossible. I can’t even imagine that. Yahyah ain’t about that life.

“Yahyah is not the kind of [person] who would do this. By any means, he is not that kind of [person].”

The man said he knew Farroukh from his hometown at Daraa, south of Damascus, where he said Farroukh’s family had a bakery. “He is from a good and well-known family in Syria,” he said, adding that Farroukh would often visit his house.

He said they first met when they were about 14 years old and he knew of no particular reason that Farroukh would have been involved in a terror attack, saying he was a “peaceful man – that’s why I’m getting shocked”.

Asked about religion or politics, he said: “We never talked about these things. We used to play football. Hopefully, he is not involved in what happened.”

In 2009 Penelope and Ronald Jones were awarded MBEs for services to children and families. Neighbours said they believe the couple had recently experienced difficulties with one of the young people they were caring for.

Farroukh moved out of the couple’s home several months ago to a house in Staines, near Heathrow airport in west London, which was also searched by police on Sunday.

A police officer stands by a barrier cordon outside an address in Sunbury-on-Thames, London. Photograph: Will Oliver/EPA

His social media communications feature a series of photographs taken at landmarks across London and the south-east, and suggests that he arrived in the UK via Egypt and Italy. His father died in Egypt last month.

West Thames College said Farroukh had enrolled to study English in December 2013.

The 18-year-old suspect was detained on Saturday morning in the departure area of Dover ferry port. Ian Harvey, the leader of Spelthorne borough council, which includes Sunbury, said he understood this man was an Iraqi who had arrived in the UK aged 15, following the deaths of his parents.

Tourist Daniel Vaselicu said the man appeared calm as officers questioned him for 10 minutes in the empty ferry departure lounge before arresting him.

The previous day, CCTV had captured images of a young man carrying a Lidl shopping bag in the street next to the Jones’s home at 6.50am on Friday 15 September.

At 8.20am, a bucket bomb left in a Lidl bag partly detonated inside a tube train carriage at Parsons Green in west London.

The District line train was packed with commuters and schoolchildren. Thirty people were injured, some with flash burns, and others as they leapt from the train.

Bomb disposal experts said photographs of the smouldering remains of the device on the train showed that the initiating charge had exploded, but had failed to detonate the main charge.

Meanwhile, a vivid description of the aftermath of the event emerged in an interim report from Transport for London (TfL), obtained by BBC London.

The TfL author describes how the station supervisor at Parsons Green first became aware that something was wrong when passengers flooded through the station, vaulting barriers.

After opening the barriers, the supervisor went to the platform: “The stairs were so busy and people were being trampled on by those pushing from behind to exit the platform.”

A mayday call from the train driver was received by the driver of a train travelling in the opposite direction, the report says, but “initial communications were hampered between the service controller and the train operator due to the incident ... a scene of confusion and distress was observed via the CCTV, with a large [number] of customers observed running towards the exit and on to the track”.

After the terror attack, the government announced that the public threat assessment was being raised to critical, signalling concern that a new attack was imminent. Following the arrest of the 18-year-old it was reduced to severe.

Announcing the move, the home secretary, Amber Rudd, said it was too early to conclude whether the attack was the work of one person.